Page:A Voyage in Space (1913).djvu/171

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These are not the actual distances, but they are so close to them that the extra convenience of being able to remember them or to write them down out-weighs the disadvantage of inaccuracy for many purposes.

The law which helps us to remember them was first stated by a man called Titius, and we ought to call it by his name if every one had his rights; but Bode made a sensational use of the law, and so it is generally known as Bode's Law. You can easily see what it amounts to: write down a set of 4's, Saturn: photographed by Barnard in 1911, with the 5-foot Reflector on Mount Wilson. and add to them other numbers which are doubled every time, beginning with 3 for Venus. The easiest way to remember it is to try and remember that the Earth's distance comes out 10; and perhaps also that Saturn is 100; from these two facts you could recover the law if you had forgotten it.

Let us spend a moment or two on the use made of the law by Bode, about the end of the eighteenth century. At that time there was a break in the series, for none of the minor planets had been found. Nowadays we know nearly 1000 of these little bodies; many of them are very tiny, only a few miles in diameter. They are probably made of the same kind